1. Field of the Invention
The present invention relates to a method of evaluating the imaging performance of a projection optical system, a method of adjusting the imaging performance, an exposure apparatus having a function which implements each of the methods, and a memory medium for controlling each of the methods.
2. Description of the Related Art
An exposure apparatus which projects the pattern of an original onto a substrate, thereby exposing the substrate is used in lithography for manufacturing a device such as a semiconductor device. In recent years, along with further miniaturization of device patterns, a demand for improving the resolution of the exposure apparatus is increasing.
To improve the resolution of the exposure apparatus, the NA of the projection optical system is increasing. These days, an exposure apparatus having an NA of 0.90 or more, and an immersion lithography technique of attaining an effective NA of 1.0 or more by filling the space between the substrate and the final surface of the projection optical system with a medium having a refractive index of 1.0 or more have been put to practical use.
Along with an increase in the NA, the polarization state of incident light on the projection optical system exerts a significant influence on the resolution. Under the circumstance, a technique of controlling the polarization state (the polarization state includes non-polarization in a broad sense) of the incident light has been proposed in order to attain a higher resolution.
However, in practice, optical elements (including optical elements of the projection optical system and illumination optical system, an antireflection film, a reflection film, a reticle, a pellicle, and a resist) which change the polarization state are located in the optical path. For this reason, an image may not be formed on the substrate with a targeted polarization state.
Examples of the factors that make the optical elements change the polarization state are the intrinsic birefringences of crystal glass materials, residual stresses imparted to an optical system material, reticle, and substrate upon manufacturing them, stress birefringences generated upon holding them, and polarization differences in the reflection/transmission characteristics of the pellicle, resist, antireflection film, and reflection film.
Japanese Patent Laid-Open No. 2006-237109 discloses a method of evaluating the relationship between the distribution of the polarization state in the pupil of an optical system including an imaging optical system and the imaging performance of the imaging optical system. Japanese Patent Laid-Open No. 2006-173305 discloses a method of adjusting the aberration of the projection optical system in response to a change in the polarization state in the illumination system.
In considering diffraction of the light by the original (reticle), it is difficult to precisely calculate the imaging performance of the projection optical system unless it is assumed that the light enters the projection optical system even from a region other than an effective light source region (a region having a light intensity higher than a predetermined value in the pupil of the illumination optical system).
However, Japanese Patent Laid-Open Nos. 2006-237109 and 2006-173305 neither disclose nor suggest a method of evaluating the imaging performance of the projection optical system on the above-mentioned assumption.